Field of the Invention
The present invention is directed to compressor valve arrangements, and is particularly applicable to gas compressors which are used on or with internal combustion engines. The present invention will in the main be described with respect to compressor discharge valves. It is however to be appreciated that the invention is also applicable to compressor intake valves.
Compressor valves generally control the flow of to and from the compression chamber of a compressor. Compressor valves of the type having a flexible valve member in the form of a valve disc or a series of valve petals are commonly used as intake and discharge valves in small capacity compressors. The single flexible valve disc, flexible valve petals, or any other flexible valve arrangement close off a number of intake or discharge ports in a seat or valve plate of the compressor valve. Compressed gas exits though the discharge ports and is admitted through the intake ports by deflecting the valve member away from the ports.
The periodic deflection of the valve member due to the operation of the compressor causes the valve member to vibrate in different modes. Under certain conditions, the vibration of the valve member can generate a significant amount of noise. For example, where the compressor is a gas compressor for supplying pressurised air to a dual fluid fuel injection system of an internal combustion engine, the discharge valves are often a source of an annoying high pitched xe2x80x9cchirping noisexe2x80x9d during low speed operation of the compressor. Where the compressor is driven off a crankshaft of the engine, this typically equates to idle and low speed engine operation and as such may be particularly objectionable to the operator.
Where the valve member is a single flexible disc or plate, it has been found that when the member is vibrated in an axi-symmetric mode, it can be idealized as a monopole sound source which is an efficient sound radiator. In this mode of vibration, different elements of the surface of the member vibrate together at least substantially in phase. Therefore, the pressure waves produced by the different elements of the member reinforce each other as they are in phase. A similar effect occurs where the valve member includes a series of valve petals when the petals vibrate together at least substantially in phase thereby also behaving as an efficient sound radiator. The vibration of the valve member in the above described manner can result in the generation of sound at relatively high levels and at particular frequencies.
The sound produced by the vibration of the valve member is however significantly reduced when, in the case of the flexible disc, the various areas of the disc are vibrating in a non-axi-symmetric mode, with the disc surface separated into areas moving at least substantially out of phase with respect to each other. In this mode of vibration, the valve disc can be idealised as a dipole sound source which is an inefficient sound radiator. This is because the pressure waves produced by the vibration of the various elements of the disc area generally cancel each other out when they are out of phase. A similar effect occurs where the valve member includes a series of valve petals when the petals do not vibrate in phase.
As the noise generated by a vibrating valve member can be particularly annoying to people close to the compressor, and may contribute to increasing the overall noise level of the compressor and/or the machine or engine to which it is operatively connected, it would be advantageous to be able to minimise or eliminate such noise.
It is therefore an object of the present invention to reduce or eliminate noise generated by a compressor valve due to valve member vibration.
With this in mind, according to the present invention, there is provided a compressor valve comprising at least one valve port opening and a flexible valve member located over the at least one valve port for controlling gas flow therethrough, wherein the compressor valve is adapted to cause elements of the valve member to vibrate at least substantially out of phase during operation of the compressor valve.
The elements of the valve member may be constituted by a plurality of individual valve portions which are joined or which together define the valve member. Alternatively, the valve member may be a single structure wherein the elements thereof are constituted by different points of the surface of said structure. Accordingly, where the valve member comprises a plurality of individual valve elements, the compressor valve may be adapted to cause these separate valve elements to vibrate substantially out of phase with respect to each other. Alternatively, where the valve member is a single structure, the compressor valve may be adapted to cause different elements of the surface of said structure to vibrate substantially out of phase with respect to each other.
The out of phase movement of the valve member may be induced by modifying or controlling the airflow around the vibrating valve member. As one possibility, the nature of the forcing air which acts to urge the valve member off its seat may be modified by way of the design and configuration of the ports and any associated passages which deliver air to the valve member. As an alternative possibility, the nature of the cushioning air or effect which acts on the other side of the valve member may be modified in a manner which results in the elements of the valve member vibrating at least substantially out of phase with respect to each other.
In yet a further alternative possibility, the physical characteristics of the valve member or the means by which it is operatively retained could be selected such as to induce the out of phase vibration of elements of the valve member. Such characteristics may include the shape, construction and/or properties of the valve member.
For example, the valve member may comprise elements of varying stiffness such that the elements of the valve member vibrate with different phases with respect to each other during operation of the compressor valve. Alternatively, separate means may be provided to vary the stiffness distribution in different elements of the valve member.
Alternatively, the valve member may be mounted in a manner so as to limit the movement of some of the elements of the valve member such that they are forced to vibrate at least substantially out of phase with respect to one another by virtue of the air flow through the compressor valve.
It is also envisaged that the compressor valve may include a combination of the above described features to induce phase difference in the vibration of the elements of the valve member. Hence, the compressor valve arrangement is effectively preventing the occurrence of the modes of vibration which are efficient at radiating sound and/or supporting those modes of vibration which are inefficient at radiating sound and which will hence promote sound cancellation and the elimination or reduction of noise generation.
Conveniently, the valve member may be in the form of a single flexible disc or any other planer element, such as a rectangular plate. Alternatively, the valve member may comprise a plurality of valve petals. The compressor valve may be of the type where the valve member is located in a gap provided between a valve seat or valve plate and a guide member.
According to a preferred embodiment of the present invention, the compressor valve may include a flexible valve disc, a valve seat, and a guide member, the valve disc being supported at a central portion thereof within a gap provided between the valve seat and the guide member, the valve seat having at least one port extending therethrough, the valve disc closing off the at least one port, wherein the at least one port is located relative to areas of the disc such that the areas of the valve disc are adapted to vibrate at least substantially out of phase with respect to each other during operation of the compressor valve.
A single port may be located eccentrically relative to the centre of the valve disc. It is also envisaged that a plurality of ports may be provided radially about the central portion of the valve disc along a portion of the periphery of the valve disc. Alternatively, the radially located ports may be staggered in a non-uniform manner about the central portion of the valve disc and/or may be of non-uniform size.
As a result, as the compressed air or other gas produced by the compressor exits through the port(s) to deflect the valve disc when in use, a non axi-symmetric pressure force is applied to the valve disc. The different areas or elements of the valve disc therefore vibrate at least substantially out of phase with respect to one another due to the difference in pressure applied to different areas of the valve disc.
According to another preferred embodiment of the present invention, the compressor valve may include a flexible valve disc, a valve seat, and a guide member, the valve disc being supported at a central portion thereof within a gap provided between the valve seat and the guide member, the valve seat having at least one port extending therethrough, the valve disc closing off the at least one port, wherein the guide member is located within the compressor valve to thereby define a flow path through the compressor valve leading to a non axi-symmetric gas flow across the valve disc when the compressor valve is in use such that areas of the valve disc are adapted to vibrate at least substantially out of phase with respect to each other during operation of the compressor valve.
Preferably, the guide member may block off at least a portion of a peripheral gap provided around the periphery of the guide member. Alternatively, the guide member may have a face facing or bearing upon the valve disc, wherein the guide member can abut and prevent movement of a section of the valve disc to thereby physically prevent an axi-symmetric mode of movement of the valve disc.
According to a further preferred embodiment of the present invention, the compressor valve may include a valve member having a series of flexible valve petals, a valve seat and a guide member, the valve petals being located within a gap provided between the valve seat and the guide member, each valve petal closing off a respective port of the valve seat, the guide member having an aperture respectively located over at least one of the valve petals wherein the gas flow across each valve petal is thereby caused to force the valve petals to vibrate at least substantially out of phase with respect to each other.
Conveniently, an aperture may be located over each valve petal. Therefore, each aperture may be located in a non-symmetric manner relative to a central elongate axis of the associated valve petal. The effect of the non-symmetric or eccentric placement of the aperture is to provide an uneven cushioning effect on the petal when there is gas flow through the compressor valve, the uneven or offset cushioning effect resulting in a twisting of the valve petal rather than an even lift off the valve seat. This effect may also be achieved by providing a valve member having valve petals which are eccentric or non-symmetric in shape relative to any main axis thereof. These arrangements assist in preventing any in phase vibration of the valve petals.
According to a yet another preferred embodiment of the present invention, the compressor valve may include a valve member having a series of flexible valve petals, a valve seat and a guide member, the valve petals being located within a gap provided between the valve seat and the guide member, wherein stiffness of the valve petals may be made to vary such that the natural frequencies of the valve petals are caused to differ, the valve petals thereby vibrating with a phase difference with respect to each other.
Preferably, the compressor valve may include a spacer located between the valve member and the guide member. The spacer may have a series of fingers of varying length, each finger being operatively arranged over a respective valve petal to thereby vary the stiffness of the petal. That is, the effective stiffness of the valve petal typically increases with increasing length of the associated finger. Accordingly, this provides for different natural frequencies for each of the petals of the valve member and hence the petals are induced to move with different phases with respect to one another.
Alternatively, the effective stiffness of the individual valve petals may be made to differ by providing petals of different widths, shapes or configurations.
According to a further aspect of the present invention, there is provided a compressor valve comprising at least one valve port and a valve member for opening and closing said port under fluid pressure, said valve member constructed so as to, in operation, vibrate with self attenuating noise characteristics.
The self attenuating noise characteristics may comprise vibration of said valve member in a non-symmetric mode. This non-symmetric mode may comprise a non-axi-symmetric mode.
In the above described compressor valve, the valve member may comprise a flexible disc having an axis, said disc being anchored relative to at least one valve port about said axis whereby, in operation, peripheral edges of said disc open and close said port. At least a portion of said peripheral edge may be anchored relative to said valve port. Alternatively, the peripheral edge may be anchored relative to said valve port along an axis of said disc. The disc may be anchored by a guide member.
In an alternative arrangement in the above described compressor valve, the valve member may comprise an elongate member having first and second ends, said valve member being cantilevered relative to a valve port at, or near, said first end thereof whereby, in operation said second end of said valve member operates to open and close said valve port. The valve member may vibrate, in operation, about an elongate axis thereof.
In all of the described embodiments, the various elements of the valve member are forced to vibrate out of phase or at least with a phase difference with respect to each other. This results in a cancellation effect on the pressure waves generated by the vibration of the elements of the valve member. The result is that the compressor valve according to the present invention is significantly quieter than known compressor valves having flexible valve members.